It is known to use quaternary ammonium salts derived from heterocyclic nitrogen-containing compounds such as pyridine, quinoline, isoquinoline, or quinaldine, as galvanic additives in acid nickel baths. The nickel coats produced by use of these additives are frequently brittle or show mat zones in their low current density regions, and thus do not meet the demands made on them.
Furthermore, it is known to use reaction products of heterocyclic nitrogen-containing compounds of the aromatic type with sultones as leveling agents in galvanic nickel baths. These products represent, on the basis of their chemical constitution, inner salts of aminoalkane sulfonic acids, so-called sulfobetaines. The leveling effect of these products is quite satisfactory; however, they are subject to decomposition under certain circumstances, which may impair the leveling effect.
The problem has therefore been to find products which likewise yield satisfactory leveling effects without being relatively susceptible to decomposition in the acid galvanic nickel bath. Applicants have surprisingly developed pyridinium sulfate compounds that function as suitable leveling agents in acid galvanic nickel baths and have satisfactory decomposition properties. In addition, the pyridinium sulfate compounds developed have the advantage of simple preparation that does not require propane sultone.